The present invention pertains to the field of chemical and oil refining processes. In particular, the invention relates to the processes of vacuum distillation of liquid mixtures, which are used for example for fractionation of hydrocarbon liquids, and relates directly to the separation of liquid mixtures.
The invention can be applied in the petrochemical industry for oil stock rectification as well as in chemical, food, pharmaceutical and other industries.
The following methods that are used in oil refining for producing a vacuum are known (see, for example, "Oil technology", the book of L. I. Gurevitch, part 1, Gostoptechizdat, 1952, pages 267-268):
A mechanical method (by dry and wet displacement and rotary pumps); PA1 A physical method based on the instantaneous condensation of the water steam, passing from the top of a column, in a surface or mixing condenser; PA1 A method based on usage of kinetic energy of an active liquid jet in ejectors etc. PA1 condensation of vapors outgoing from a mass-transfer column, suction of non-condensable gases by a vacuum-producing system, which is connected to a vacuum pump and is composed of an absorber, a phase separator and a cooler, connected in series, separation of a liquid phase with the lowest solidification temperature in the phase separator, cooling of the liquid phase after the separation to a temperature which is not lower than the solidification temperature of this liquid, use of the cooled liquid phase as an absorbent for condensation of the vapors and for producing a vacuum.
A combination of some of the above mentioned methods is used in the method for vacuum processing of a fuel oil introduced in SU (A. C CCCP) No. 1447637, M. cl. C10 G 7/06, 1967.
According to this method a heated-up fuel oil is rectified under vacuum in a vacuum column. The method includes withdrawing of side-cut distillates from the column, bleeding of non-condensable gases and vapors from the top of the column, feeding of the vapors back into the bottom of the column for additional extraction of a distillate fraction under vacuum in the presence of non-condensable gases and vapors of the vacuum column, and condensation and absorption of the distillate fraction, extracted from the residue, by a chilled mixture of the lower side-cut distillate of the vacuum column and distillate fraction.
An imperfection of this method is incomplete utilization of energy of the chilled liquid for condensation of the vapors. That is why a deeper vacuum can not be obtained and the output of the distillate fractions can not be increased.
The closest analogue of the present invention is a method for producing vacuum in mass-transfer columns, wherein suction of un-condensed gases from the top of a column is effected by a chilled reflux, generated as a result of condensation of outgoing hydrocarbon vapors. The hydrocarbon vapors pass from the mass-transfer column into surface condensers. A reflux, generated in the condensers as a result of condensation of the hydrocarbon vapors, drains into a collector. A part of the reflux is fed back into the column for refluxing. A jet pump imparts pressure energy to those parts of the reflux, which ensures suction of gases. After cooling in a cooler the reflux is fed into an ejector, which evacuates gases from the condensers. A mixture of the un-condensed gases and reflux is separated in a separator. The gases are released to the atmosphere or bled for processing (or purification), the reflux passes to the collector for further delivery to the ejector by the jet pump (see SU (A. C CCCP) No. 1019645, M. cl. B01 D 3/00, 1993).
The main imperfection of the analogue method is the necessity to use the total amount of the cooled reflux, condensed from the outgoing vapors, for suction of non-condensable gases. This results in repeated contamination of the reflux by impurity components of the gases and vapors outgoing from the top of the column and consequently in deterioration of the quality of the base distillates so that additional expenses for depuration of the distillates are required.